OPP 9615011 Crowley Abstract The geologic record indicates that the earth has been subject to four main phases of glaciation in the last one billion years: the late Cenozoic, Carboniferous, Ordovician, and Late Precambrian. In order to develop a uniform theory for glacial periods it is necessary to identify the factors responsible for both general conditions of glacial inception and growth and retreat of the ice sheets. Over the last several years our modeling group has succeeded in identifying plausible boundary conditions for glacial inception for the pre-Cenozoic glacial ages. Separately W. R. Peltier and colleagues have succeeded in simulating the evolution of ice volume during the last glacial cycle with an ice sheet model coupled to a two-dimensional energy balance model (EBM). This award supports a project to combine these separate lines of research in order to test whether an ice sheet model developed for Pleistocene studies can, without any additional tuning, yield changes in ice volume consistent with evidence from the Carboniferous and Ordovician glacial periods. This research will entail conducting a suite of experiments with the Peltier model that involve forcing the model with temperature and (parameterized) moisture fields from EBMs with the model run through a series of orbital insolation changes. The objective is to determine whether the paleo ice sheet grows to dimensions commensurate with geological data and also whether "hot" summer orbits melt the ice sheet. To test for robustness of results, some of the experiments will be repeated using temperature and precipitation fields generated by a general circulation model. If this work is successful in simulating the Carboniferous and Ordovician glaciations, confidence will be enhanced in the ice sheet model and a significant step will have been taken in developing a uniform explanation for glacial periods in earth history.
